Their legs are positioned more vertically beneath their bodies than are the sprawling legs of reptiles and pelycosaurs. The feet were more symmetrical, with the first and last toes short and the middle toes longer, an indication that the foot's axis was placed parallel to that of the animal, not sprawling out sideways. This would have given a more mammal-like gait than the lizard-like gait of the pelycosaurs.[5]

Therapsids' temporal fenestrae are greater than those of the pelycosaurs. The jaws of some therapsids are more complex and powerful, and the teeth are differentiated into frontal incisors for nipping, great lateral canines for puncturing and tearing, and molars for shearing and chopping food.

Like all land animals, the therapsids were seriously affected by the Permian–Triassic extinction event; the very successful gorgonopsians dying out altogether and the remaining groups - dicynodonts, therocephalians, and cynodonts - reduced to a handful of species each by the earliest Triassic. The dicynodonts, now represented by a single family of large stocky herbivores, the Kannemeyeridae, and the medium-sized cynodonts (including both carnivorous and herbivorous forms), flourished worldwide throughout the Early and Middle Triassic. They disappear from the fossil record across much of Pangea at the end of the Carnian (Late Triassic), although they continued for some time longer in the wet equatorial band and the south.

The therocephalians, relatives of the cynodonts, managed to survive the Permian-Triassic extinction and continued to diversify through the Early Triassic period. Approaching the end of the period, however, the therocephalians were in decline to eventual extinction, likely out competed by the rapidly diversifying Saurian lineage of diapsids, equipped with sophisticated respiratory systems better suited to the very hot, dry and oxygen-poor world of the End-Triassic.